Methods and apparatus for mold mitigation in fuel cell humidifiers

Abstract

Methods and apparatus for reducing the tendency for mold formation and accumulation in membrane-based humidifiers used in PEM fuel cell systems can include reducing the oxygen concentration and/or generating hydrogen peroxide within the humidifier upon shutdown of a fuel cell system. In some embodiments, a fuel cell system comprises valves and lines located and operable to facilitate introduction of hydrogen into the humidifier upon shutdown of the system. In some embodiments, a fuel cell humidifier comprises a catalyst for promoting the generation of hydrogen peroxide from hydrogen and oxygen, and/or comprises acidic gas transport layers.

What is claimed is: 
     
         1 . A method of operating a fuel cell system, said fuel cell system comprising:
 a humidifier having a dry-side compartment and a wet-side compartment, said dry-side compartment separated from said wet-side compartment by a water transfer membrane; and   a fuel cell stack comprising an anode compartment and a cathode compartment, said anode compartment separated from said cathode compartment by a proton-exchange membrane;   wherein, in an electrical power-producing mode of operation, said method comprises:   supplying hydrogen to said anode compartment of said fuel cell stack;   supplying air to said cathode compartment of said fuel cell stack via said dry-side compartment of said humidifier;   discharging oxygen-depleted air from said cathode compartment of said fuel cell stack, and directing it through said wet-side compartment of said humidifier, whereby said air supplied to said cathode compartment of said fuel cell stack is humidified by said oxygen-depleted air discharged from said cathode compartment of said fuel cell stack; and   drawing electrical power from said fuel cell stack; and   wherein, in a shutdown mode, said method comprises:   interrupting supplying hydrogen to said anode compartment of said fuel cell stack;   interrupting supplying air to said cathode compartment of said fuel cell stack; and   allowing hydrogen to diffuse from said anode compartment to said cathode compartment of said fuel cell stack via said proton-exchange membrane, and from said cathode compartment of said fuel cell stack to said dry-side compartment of said humidifier and to said wet-side compartment of said humidifier, whereby at least a portion of said diffused hydrogen reacts to consume oxygen in said cathode compartment of said fuel cell stack,   wherein said supplying hydrogen to said anode compartment of said fuel cell stack comprises supplying hydrogen to said anode compartment of said fuel cell stack from a hydrogen supply via a fuel recirculation loop,   wherein, in said shutdown mode, said method comprises providing hydrogen from a fuel supply to at least one of said dry-side compartment or said wet-side compartment of said humidifier,   wherein said hydrogen is supplied from said fuel supply to at least one of said dry-side compartment or said wet-side compartment of said humidifier via a line that bypasses said fuel cell stack.   
     
     
         2 . The method of  claim 1  wherein interrupting supplying air to said cathode compartment of said fuel cell stack comprises closing a first valve positioned upstream of said dry-side compartment of said humidifier. 
     
     
         3 . The method of  claim 1  wherein allowing hydrogen to diffuse from said anode compartment to said cathode compartment of said fuel cell stack via said proton-exchange membrane, and from said cathode compartment of said fuel cell stack to said dry-side compartment and to said wet-side compartment of said humidifier, comprises closing a second valve positioned downstream of said wet-side compartment of said humidifier. 
     
     
         4 . The method of  claim 1  wherein at least one of said dry-side compartment or said wet-side compartment of said humidifier comprises a catalyst for promoting formation of hydrogen peroxide from oxygen and hydrogen during said shutdown mode. 
     
     
         5 . The method of  claim 1  wherein at least a second portion of said diffused hydrogen reacts to consume oxygen in said dry-side compartment and said wet-side compartment of said humidifier. 
     
     
         6 . The method of  claim 1  wherein said interrupting supplying air to said cathode compartment of said fuel cell stack is performed prior to said interrupting supplying hydrogen to said anode compartment of said fuel cell stack. 
     
     
         7 . The method of  claim 1  wherein, in said shutdown mode, said method comprises providing a fluid connection between said fuel recirculation loop and at least one of said dry-side compartment or said wet-side compartment of said humidifier. 
     
     
         8 . The method of  claim 7  wherein providing said fluid connection between said fuel recirculation loop and at least one of said dry-side compartment or said wet-side compartment of said humidifier comprises opening a valve between said fuel recirculation loop and said humidifier. 
     
     
         9 . A fuel cell system comprising:
 a fuel cell stack;   an oxidant supply device for supplying air to said fuel cell stack;   a humidifier for humidifying air supplied by said oxidant supply device to said fuel cell stack, said humidifier having a dry-side compartment and a wet-side compartment, wherein said dry-side compartment and said wet-side compartment are separated by a water transfer membrane;   a first air supply line between said oxidant supply device and said dry-side compartment of said humidifier;   a second air supply line between said dry-side compartment of said humidifier and an oxidant inlet of said fuel cell stack, for directing humidified air from said humidifier to said fuel cell stack;   a first exhaust line connected between an oxidant outlet of said fuel cell stack and said wet-side compartment of said humidifier, for supplying an oxidant exhaust gas discharged from said fuel cell stack to said wet-side compartment of said humidifier to humidify air supplied by said oxidant supply device to said fuel cell stack;   a second exhaust line for discharging an exhaust stream from said wet-side compartment of said humidifier;   a first valve installed in said first air supply line, wherein said first valve is for selectively opening and closing said first air supply line; and   a second valve installed in said second exhaust line wherein said second valve is for selectively opening and closing said second exhaust line,   wherein said humidifier comprises an acidic gas transport layer positioned adjacent at least one side of said water transfer membrane.   
     
     
         10 . The fuel cell system of  claim 9  wherein said humidifier comprises a catalyst for promoting formation of hydrogen peroxide from hydrogen and oxygen. 
     
     
         11 . The fuel cell system of  claim 10  wherein said catalyst is located on both said wet-side compartment and said dry-side compartment of said humidifier. 
     
     
         12 . The fuel cell system of  claim 10  wherein said catalyst is deposited on a gas transport layer positioned adjacent said water transfer membrane on said wet-side compartment and/or on said dry-side compartment of said humidifier. 
     
     
         13 . A fuel cell system comprising:
 a fuel cell stack;   an oxidant supply device for supplying air to said fuel cell stack;   a humidifier for humidifying air supplied by said oxidant supply device to said fuel cell stack, said humidifier having a dry-side compartment and a wet-side compartment, wherein said dry-side compartment and said wet-side compartment are separated by a water transfer membrane;   a first air supply line between said oxidant supply device and said dry-side compartment of said humidifier;   a second air supply line between said dry-side compartment of said humidifier and an oxidant inlet of said fuel cell stack, for directing humidified air from said humidifier to said fuel cell stack;   a first exhaust line connected between an oxidant outlet of said fuel cell stack and said wet-side compartment of said humidifier, for supplying an oxidant exhaust gas discharged from said fuel cell stack to said wet-side compartment of said humidifier to humidify air supplied by said oxidant supply device to said fuel cell stack;   a second exhaust line for discharging an exhaust stream from said wet-side compartment of said humidifier;   a first valve installed in said first air supply line, wherein said first valve is for selectively opening and closing said first air supply line; and   a second valve installed in said second exhaust line wherein said second valve is for selectively opening and closing said second exhaust line;   a fuel supply device and a fuel recirculation loop for circulating a fuel through said fuel cell stack; and   a fuel bleed line fluidly connecting said fuel recirculation loop to said first exhaust line, said fuel bleed line comprising a purge valve for selectively bleeding fuel from said fuel recirculation loop into said wet-side compartment of said humidifier via said first exhaust line.   
     
     
         14 . The fuel cell system of  claim 13  wherein said humidifier comprises a catalyst for promoting formation of hydrogen peroxide from hydrogen and oxygen. 
     
     
         15 . The fuel cell system of  claim 14  wherein said catalyst is located on both said wet-side compartment and said dry-side compartment of said humidifier. 
     
     
         16 . The fuel cell system of  claim 14  wherein said catalyst is deposited on a gas transport layer positioned adjacent said water transfer membrane on said wet-side compartment and/or on said dry-side compartment of said humidifier. 
     
     
         17 . A fuel cell system comprising:
 a fuel cell stack;   an oxidant supply device for supplying air to said fuel cell stack;   a humidifier for humidifying air supplied by said oxidant supply device to said fuel cell stack, said humidifier having a dry-side compartment and a wet-side compartment, wherein said dry-side compartment and said wet-side compartment are separated by a water transfer membrane;   a first air supply line between said oxidant supply device and said dry-side compartment of said humidifier;   a second air supply line between said dry-side compartment of said humidifier and an oxidant inlet of said fuel cell stack, for directing humidified air from said humidifier to said fuel cell stack;   a first exhaust line connected between an oxidant outlet of said fuel cell stack and said wet-side compartment of said humidifier, for supplying an oxidant exhaust gas discharged from said fuel cell stack to said wet-side compartment of said humidifier to humidify air supplied by said oxidant supply device to said fuel cell stack;   a second exhaust line for discharging an exhaust stream from said wet-side compartment of said humidifier;   a first valve installed in said first air supply line, wherein said first valve is for selectively opening and closing said first air supply line;   a second valve installed in said second exhaust line wherein said second valve is for selectively opening and closing said second exhaust line;   a fuel supply device and a fuel recirculation loop for circulating a fuel through said fuel cell stack; and   a fuel bypass line fluidly connecting at least one of said wet-side compartment or said dry-side compartment of said humidifier to a fuel supply, said fuel bypass line comprising a valve for controlling supply of fuel from said fuel supply to said humidifier.   
     
     
         18 . The fuel cell system of  claim 17  wherein said humidifier comprises a catalyst for promoting formation of hydrogen peroxide from hydrogen and oxygen. 
     
     
         19 . The fuel cell system of  claim 18  wherein said catalyst is located on both said wet-side compartment and said dry-side compartment of said humidifier. 
     
     
         20 . The fuel cell system of  claim 18  wherein said catalyst is deposited on a gas transport layer positioned adjacent said water transfer membrane on said wet-side compartment and/or on said dry-side compartment of said humidifier.